1. Field of the Invention
This invention relates generally to the multiple tessellation folding of sheet materials, and is more particularly concerned with the methodology of and apparatus for folding these patterns in a one step continuous operation.
2. Discussion of the Prior Art
Sheet materials can be tessellation folded in an infinite variety of patterns, and the patterns can be arranged into different classes of patterns. The patterns are best viewed by class, although particular patterns are hybrids, as they involve a combination of classes.
Plaiting is the simplest and best known class of tessellation folding pattern. Most often it is based on a single system of equally spaced parallel folding lines, but more complex plaiting patterns are formed by varying the spacings and/or the inclinations between the folding lines. In general, therefore, plaiting can be defined as a tessellation folding pattern based on a single system of more or less parallel, but continuously straight, folding lines.
Traditionally, craft plaiting is done by placing the sheet material to be folded conjugatively between two master sheets of stiff paper (or like material) which have been previously folded in the plaiting pattern wanted, and have subsequently been opened out. The folds in such master sheets generally retain some weak folding bias which prevents the sheets from being truly flattened out and assists in refolding for several repeat foldings before the folding bias disappears. The sandwich (the two master sheets with the sheet material between them) is manually folded to complete collapse in order to set the folds. Heat may be applied during pressing to heat-set the folds when plaiting certain fabrics.
There are several types of plaiting machines available for plaiting in a production setting.
Tessellation folding patterns of significant interest are more complex than plaiting patterns. They are based on having two systems of more or less parallel folding lines crossing one another, either orthogonally or obliquely; they could also be defined as patterns in which four folding lines meet at each folding focus (or intersection). This form of tessellation patterning is often called "cross plaiting" on the basis of assuming that plaiting takes place independently in each system, and the tessellation pattern developed is an interference pattern generated by meeting of the two plaitings. But the assumption is not entirely valid because, in folding, the two systems are not wholly independent of each other. Even so, as in single system patterning, the spacings and inclinations of the folding lines in each of the systems can be varied.
In triple system tessellation folding, three systems of parallel folding lines intersect. They could also be defined as patterns in which six folding lines meet at each folding focus.
Although the art of single system tessellation folding (plaiting) is of contextual interest, it is well established and known. Thus, references to such art is made only where it has particular relevance, e.g. in hybrid pattern folding.
U.S. Pat. No. 1,571,105 to Burdick discloses a machine for single system folding small sheets of paper (e.g. paper money) by threading the paper between several horizontally disposed contiguous, but untouching, pairs of plates. At each end the plates are mounted on the pivots of chain link pantographs so that, as the chain link pantographs are shortened by compression, the pairs of plates rotate and take up a vertical and closely spaced side-by-side configuration. In so doing, the paper threaded between the plates is plait folded. U.S. Pat. No. 2,709,950 to Foster et al. discloses a machine for tessellation folding a paper tube into a dual system polygonal bellows. It is done by pressing the tube, all at once, with arrays of blades extending along its length, causing folding to take place at the contact locality of each blade. The tube shortens as folding takes place; and, so that the blades move in concert with the tube as it shortens, the blades are mounted on the pivots of a chain link pantograph.
U.S. Pat. No. 2,826,239 to Villoresi, discloses several related methods of making tessellated papers for packaging purposes. These are formed in a two step process. In the first, the paper is run between heated impressing rolls having intermeshing chevron teeth. This gives the paper dual system folding bias so that, in the second step, when the material confined between the sides of a squeeze box is compressed laterally (also transversally in a variant form), varying degrees of dual system tessellation folding is induced. A method of longitudinally scoring of paper, alternately on its top and bottom sides, is also disclosed as a means of enhancing the degree of dual system folding obtained when the material is subjected to compression in the squeeze box.
U.S. Pat. No. 2,901,951 to Hockfeld discloses a two step method of dual system tessellation folding a sheet material by first applying single system folding, and then applying plait shaped dies to upset the pleats to cause them to fold locally with dual system tessellation folding: the dies are applied progressively as the plaited material is passed through the machine.
U.S. Pat. No. 2,950,656 to Gewiss discloses a two step method of progressively applying dual system folding to initially plaited flat and cylindrically shaped sheets. Using a feed, stop and fold repetitive mechanism, die fingers are pressed into the plaits of a single system folding, causing them to cross-fold and form a dual system folding at one set of localities at a time. A related method is also disclosed in which die fingers mounted on the pivots of link chains are inserted between the plaits of a single system folded, but partially extended, sheet material. Cam actuated bars attached to every second pivot in each of the chains ensure that, as the folding and chains are compressed and traversed through the machine, the chain links fold alternately in one direction and then the other, so that the die fingers extending from the chain pivots, cause the plaits to cross plait alternatively also in one direction and then the other, thus forming the dual system folding.
U.S. Pat. No. 3,135,174 to Gewiss discloses the use of two master sheets (made from malleable stiff paper previously folded to the dual system pattern wanted, and then opened out) to tessellation fold in two steps, the pattern on to a sheet material placed conjugatively between them. In the first step the sandwich (the two master sheets with the sheet material between them) is plaited. In the second step the plaiting is compressed longitudinally, causing dual system cross folding to take place, according to the pattern initially put on the master sheets. The patent also discloses applying the same two master sheet, two step tessellation folding method to cylindrically shaped sheets.
U.S. Pat. No. 3,553,423 to Geviss cites the use of one master sheet to perform two step dual system folding of a sheet material, and also of two sheet materials; one is conjugatively placed in contact with one side of the master sheet, and the other with the other side. Varying the thickness of the master sheet to reduce the sharpness of the foldings is also cited.
U.S. Pat. No. 5,234,727 to Hoberman discloses forming complex dual system space enclosing tessellation folding patterns, but does not disclose means of folding them.
While tessellation folding is known in the prior art, and several types of folding machines have been developed, such machines are very limited in the variety of folding patterns that can be made, and they are not very practical. Thus, no simple, broadly applicable means of production has been developed.